1. Field of the Invention
This invention relates to articles for electrical use, wholly or partly consisting out of a composition comprising an aromatic polyamide-imide and having excellent thermal resistance, humidity resistance, storage stability and electrical characteristics.
2. Description of the Prior Art
Recently, large integration and high reliability have been particularly required of electronic parts, and the development of materials having excellent thermal resistance, humidity resistance, adhesion and electrical characteristics which can be applied to the construction electronic parts has been desired, primarily because most of the known synthetic resins used for this purpose become unstable at temperatures above 250.degree. C. as their softening points are exceeded or their decomposition points approached. As such materials, the use of thermal resistance polymers may be considered. In general, however, thermal resistance polymers are insoluble in most solvents and must be used in the form of their precursors. For example, aromatic polyamide acids which are known as thermal resistance polymers are susceptible to hydrolysis and inferior in storage stability or must be converted by heat treatment into aromatic polyimides or aromatic polyamide-imides having thermal resistance at a temperature around 300.degree. C. Accordingly, these aromatic polyamide acids cannot be applied to electronic parts which are affected by heat treatment. Further, contamination is caused by the low molecular weight compounds formed upon heat treatment.
Although polyimides and polyamide-imides which are partially soluble in solvents are also known, the practical features of most of the polyimides and polyamide-imides, such as thermal resistance, humidity resistance and adhesion are inferior. Also, those polyimides and polyamide-imides synthesized at a temperature above 150.degree. C. are subject to partial hydrolysis and crosslinking, and it is difficult to obtain linear polymers having a reduced viscosity sufficient for producing the above described practical features.
Further, compositions comprising silver particles and glass frits are known as compositions possessing electrical characteristics. However, these compositions finally require firing at a high temperature of about 500.degree. to 1000.degree. C. Consequently it is difficult to obtain high accuracy and cost becomes high. Moreover, these compositions cannot be applied to substrates except thermal resistance substrates such as ceramics, nor to substrates mounted with electrical elements.